The present invention relates in general to sheet fed presses, and in particular to device for controlling the suction gripper systems arranged in sheet guiding cylinders in face and back printing machines.
In sheet fed face and back printing machines which reverse the sheet about its rear edge and which have only one sheet guiding cylinder between its printing sets, the sheet guiding cylinder is provided with a suction gripper system for engaging the rear edge of the sheet incoming from the upstream impression cylinder and for transferring the sheet to a mechanical gripper system on the subsequent impressions rendered. In order to perform this function the suction gripper system is provided with suitable drives and linkages which generate prescribed movements of the suction unit of the gripper system.
From the DDR Pat. No. 54 703, a suction system is known which is firmly mounted on a tumbler shaft and which is moved on a circular path into a swing-in and swing-out position relative to the movement of the sheet guiding cylinder.
The disadvantage of this known control device for the suction gripper system is the fact that a so-called deviation angle is formed between the upper surface of the suction head and the sheet to be disengaged from the impression cylinder during the swing-in movement of the suction gripper system when the sheet is to be transferred to the gripper system of the sheet guiding cylinder. As a result of this deviation angle, the holding force of the suction system diminishes and particularly in processing carton-like papers misplacements of the sheet from the suction head and the buckling of the sheet portion immediately adjoining the engagement surface with the suction gripper may occur.
This disadvantage takes effect especially in the case of increased pulling forces employed at higher working speeds of the printing machine and consequently orientation and registration failures may result. In the DDR Pat. No. 110 451 a suction gripper system is disclosed which is a part of a coupling member between a double rocker arm and consequently is guided on a curved path of movement of the coupling member. Due to the formation of a bulge on the sheet the pulling forces exerted by the suction gripper system are temporarily reduced. Nonetheless the problem of the aforementioned deviation angle is not solved by this prior art suction gripper control and this angle is formed similarly as in the other known suction systems. Moreover the arrangement of a suction gripper on a coupling member results in high construction expenditures.